For a stereo reproduction with a surround sound system using a multi-channel A/V amplifier, Dolby Surround System is widely known (ref. FIG. 2 in Patent Document 1).
FIG. 5 illustrates a configuration of a conventional A/V amplifier 500 using Dolby Surround System. This A/V amplifier 500 includes four channels, i.e., three channels in front and one channel in rear.
Based on 2-channel (left and right) stereo reproduction signals L and R entered into the terminals 501L and 501R, the decoder 502 produces and outputs four signals in total, i.e., the front left and right outputs 503L and 503R (stereo), the rear output 503S (monaural; in Patent Document 1, outputs from two speakers), and the center output 503C, according to the internal logic.
The above four output signals are amplified by the amplifiers 504A to 504D each provided for the respective outputs, and then sent to the speakers for each channel (in FIG. 5, only the speakers 506L for L-channel and 506R are shown) via the terminals 505A to 505D to cause the respective speakers to produce a sound, thereby achieving a reproduction by the predetermined Dolby Surround system.    [Patent Document 1] Japanese Examined Utility Model Application 6-23119